Space debris is a large problem. Most countries didn’t bother to think about it because there was no legal or financial consequences to leaving rubbish in orbit. Now in some countries there are laws so the new spacecraft have to build in a way to deorbit themselves so they don’t add to the rubbish, but old rocket booster and even paint specks float around and cause issues. And lots of countries didn’t make these kind of space laws yet. Lots of places are working on trying to fix this problem in space like at ESA Clean Space: http://blogs.esa.int/cleanspace/